Wireless communication services for mobile vehicles, such as navigation and roadside assistance, have increased rapidly in recent years. Most of the services that have been offered are for a mobile vehicle in operation, but more recently, the demands and potential for services to a turned-off vehicle have grown. Services that may be requested while the vehicle is Off or in a Standby State may include maintenance and diagnostic functions, system updates, vehicle position determination, unlocking of the doors, or vehicle alarm silencing.
Normally when the mobile vehicle is off, it is placed into a powered-down discontinuous-receive (DRx) or Standby State (also called sleep cycle). A communication device and a telematics unit on or in communication with each other and with the vehicle may also be placed into a similar DRx cycle to minimize power drain on the vehicle battery. To perform a requested function while the ignition is off, the telematics unit may be awakened, the desired function performed, and the telematics unit subsequently placed back into the DRx or Standby State. For example, a telematics unit may monitor a satellite broadcast channel for a command signal. Based on the command signal, the cellular phone of telematics unit is powered up. The telematics unit may then call a telematics service provider's call center to receive then perform a service request. Alternatively, a data message sent by the call center containing a service request, may be waiting for the telematics unit when it awakes. After performing the service, the telematics unit may return to the Standby State.
A network access device (NAD) of a telematics unit communicates with a call center. In a Standby State, the NAD dissipates low current (13 mA-20 mA) when it is awakened in an “In Service” area to have the telematics unit perform functions (e.g. unlocking the vehicle doors silencing a vehicle alarm). However, when the NAD is in a “No Service” area (e.g. underground parking garage), the NAD may dissipate more than ten times the amount of current (200 mA-300 mA). Consequently, the NAD drains the vehicle battery at a faster rate, causing the NAD to enter into Off State prematurely, thereby rendering the telematics unit incapable of performing any services and potentially leaving the vehicle battery undesirably discharged.